Back pain is the commonest cause of disability. Approximately 40% of back pain is caused by disorders of the facet joints.
The facet joints (also called zygapophysial joints or z-joints) are paired structures on the back and side of the spine. These joints support the torso during flexion, extension and rotation of the spine. These are synovial joints and therefore contain joint fluid. Joint fluid is viscous and a lubricant. Synovial cysts occur along the margins of many joints in the body. These cysts are caused by a degenerative process. Synovial cysts are lined by synovial cells.
These cysts frequently occur along the margins of the facet joint. These cysts may occur on the back (posterior) or the front (anterior) of the facet joints. The sensitive nerve structures are located on the front of the joint and therefore anterior cysts located within the spinal canal are usually symptomatic. Cysts along the back of the joints may be associated with back pain but are usually asymptomatic. When there is a cyst on the back of the joint there is usually no anterior cyst present. This is believed to be due to relative decompression of the anterior joint capsule pressure into the posterior capsule.
When these cysts enlarge into the spinal canal they cause back pain and/or radiculopathy (leg pain) by compressing the adjacent structures and nerves. These benign cysts usually are connected to the adjacent joint. In the spine these cysts usually arise from the facet joints but also may occur within the spinal ligaments rarely.
Fluid, bone, cartilage fragments and debris are frequently present in arthritic joints. Synovial cysts arise from arthritic joints.
The current treatment of synovial cysts is usually surgical. During the surgical procedure an incision is made in the back and the muscles and ligaments are cut and retracted to access the back of the spinal canal. The lamina or back of the bony spinal canal is then removed in order to access the cyst. Then the cyst is surgically removed using a scalpel, cautery or other cutting instruments. The surgical procedure is effective resulting in improvement in leg pain in the majority of patients. However surgery damages surrounding tissues, ligaments and muscles. Also surgery can result in disability due to removal of or damage to the muscle, ligaments and bony structures that mechanically support the spine and may result in spinal instability. Although surgery is usually successful cysts may recur even after a successful operation. A current trend in spinal surgery and intervention is toward tools and techniques to minimize tissue damage using image guidance and minimally invasive techniques
Percutaneous aspiration is also used to treat synovial cysts, and in particular synovial cysts located anterior to a facet joint. Instead of directly removing the cyst the joint is aspirated with a needle. Synovial fluid is very thick and often cannot be aspirated using a standard spinal needle. The results of current percutaneous methods of treatment are sub-optimal. Less than half of patients are successfully treated. Also, even when successfully aspirated the cysts may refill with joint fluid resulting in recurrence of symptoms. Therefore many percutaneous aspirations fail to resolve the patient's symptoms and patients often have to undergo a second open surgical procedure to definitively treat their pain with additional risks, expense, recovery time and pain. Direct percutaneous aspiration has traditionally not been an option for synovial cysts located anterior to facet joints.
Percutaneous ablation is used to treat facet related pain but is not used to treat facet cysts. A common method to treat facet related pain is radiofrequency ablation. The nerves supplying the facet joint are heated and this disrupts the nerve function and conduction resulting in pain relief. Also the capsule may be treated directly for treating pain. Radiofrequency energy delivered by a needle or probe is usually used for ablation although cooled probes (cryotherapy), focused ultrasound and alcohol may also be used.
There is a need for percutaneous minimally invasive devices and procedures to access the facet joint and perform various procedures in relation to the facet joint, for example to aspirate thick synovial fluid and definitively treat synovial cysts of the facet joints.